The application of LED becomes popular, and the progress of LED brightness also promotes an extensive use of LEDs. Based on years of experience on research, development and selling of the LED products, the inventor of the present invention has developed a control device for improving system stability as well as greatly simplifying the system wiring.
The design of serially connected LED lamp control device is mainly applied for the occasion of connecting a series of LED lamps, and each LED lamp is controlled effectively and independently.
Three traditional methods for controlling the serially connected LED lamps are described as follows:
The first design uses a control box to control all lamps and an electric cable to connect each of the LED lamps. The cost for such method is lower; however, if the lamps are farther apart from each other or evenly distributed or arranged, then the cost of the electric cable is very high. Furthermore, since the length for each cable is not the same, which will cause tremendous difficulty for mass production and installation. Therefore, this design was adopted only at its early stage, but is seldom used thereafter because of its disadvantages.
The second design refers to a fixed address serial connection, of which a control circuit is installed in each lamp and a fixed address ID is assigned to each lamp, such that the system can operate as long as the power supply and the signal line are connected. Such system is simpler, but it has several drawbacks. Since each lamp requires a controller, therefore the cost is higher. In addition, each lamp requires a different ID, and thus making the manufacturing more difficult. Furthermore, it is necessary to change the ID of the spare parts for repair and maintenance purposes, thus causing some troubles.
The third design adopts a serially connected control circuit, which subdivides the controller as described in the abovementioned system and installs some part of the circuit in the lamp, and then all lamps are serially connected by an electric cable. Therefore, each time is seemingly identical and thus this design can simplify the level of difficulty for wiring, installing and maintaining the whole system.
Please refer to FIG. 7 for the block diagram of the foregoing third connection method. There are only 5 lamps 101a˜101e shown in the figure, and a minimal quantity of signal wires 102, 103 is required for the system, which includes a total of six lines such as a DAT, a Clock (CLK), a latch signal (STB), an output enable (OE) for controlling the brightness, a power supply (VDD) and a ground (GND) lines. Each lamp unit 101a˜101e uses the same line to connect the signal 103. Please refer to FIG. 8 for the internal structure of the lamp units 101a˜101e as depicted in FIG. 7, which comprises 4 sets of circuits for description. In actual practice, the number of circuits depends on the actual need. In FIG. 8, the signal group 210 is an input end, and the signal group 211 is an input end of another signal, and four sets of D-type latches 203a˜203d constitute a set of S-R shift registers and are driven by the external clock signal CLKI to save the external data DATI into the latches 203a˜203d in the proper order. In the meantime, the internal data are sent to the next lamp through another data line DATO. After the data is shifted to a fixed address, the external latch signal STB 1 will be outputted from four sets of D-type latches 203a˜203d to another set of D-type latches 203a˜202d and then sent to the LED driver circuit 201 to drive the external LEDs 213a˜213c. The buffers 204, 205, 206, 207 act as the buffers for the output of the CLK signal and data, the output of DATO latch signal, the output of STBO and the brightness output OEO respectively. The four connected signals DAT, CLK, STB and OE are the minimum requirement for such system. If there is an additional required function, the quantity of connecting wires will be increased. In view of the design that subdivides the central circuit to each lamp, the level of its originality is not high.
Since the method adopted by the foregoing method requires the connection of many circuits, and the lengths of the external connecting cables are different, and different lots of ICs have a slight difference such that the signal transmission error may occur easily (which will be illustrated by FIGS. 4 to 6), therefore the inventor of the present invention based on years of experience on designing and manufacturing similar system to invent and develop the control device in accordance with the invention to greatly improve the overall system stability as well as greatly reduce the required number of circuit connections.